Variation in stem mortality rates determines patterns of above‐ground biomass in <scp>A</scp>mazonian forests: implications for dynamic global vegetation models

Michelle O. Johnson, David Galbraith, Manuel Gloor, Deurwaerder H De, Matthieu Guimberteau, Anja Rammig, Kirsten Thonicke, Hans Verbeeck, Randow C von, Abel Monteagudo, Oliver L. Phillips, Roel J.W. Brienen, Ted R. Feldpausch, Gonzalez G Lopez, Sophie Fauset, Carlos A. Quesada, Bradley Christoffersen, Philippe Ciais, Gilvan Sampaio, Bart KruijtPatrick Meir, Paul Moorcroft, Ke Zhang, E Alvarez‐Davila, de Oliveira A Alves, Ieda Amaral, Ana Andrade, Luiz E.O.C. Aragao, A Araujo‐Murakami, Eric J.M.M. Arets, Luzmila Arroyo, Gerardo A. Aymard, Christopher Baraloto, Jocely Barroso, Damien Bonal, Rene Boot, Jose Camargo, Jerome Chave, Alvaro Cogollo, Valverde F Cornejo, da Costa AC Lola, Fiore A Di, Leandro Ferreira, Niro Higuchi, Euridice N. Honorio, Tim J. Killeen, SG Laurance, WF Laurance, Juan Licona, Thomas Lovejoy, Yadvinder Malhi, B Marimon, BH Marimon, Darley C.L. Matos, Casimiro Mendoza, David A. Neill, Guido Pardo, M Peña‐Claros, Nigel C.A. Pitman, Lourens Poorter, Adriana Prieto, H Ramirez‐Angulo, Anand Roopsind, Agustin Rudas, Rafael P. Salomao, Marcos Silveira, Juliana Stropp, Steege H ter, John Terborgh, Raquel Thomas, Marisol Toledo, A Torres‐Lezama, der Heijden GMF van, Rodolfo Vasquez, Vieira IC Guimarães, Emilio Vilanova, Vincent A. Vos, Timothy R. Baker*

*Corresponding author for this work

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Abstract

<jats:title>Abstract</jats:title><jats:p>Understanding the processes that determine above‐ground biomass (<jats:styled-content style="fixed-case">AGB</jats:styled-content>) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (<jats:styled-content style="fixed-case">DGVM</jats:styled-content>s). <jats:styled-content style="fixed-case">AGB</jats:styled-content> is determined by inputs from woody productivity [woody net primary productivity (<jats:styled-content style="fixed-case">NPP</jats:styled-content>)] and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody <jats:styled-content style="fixed-case">NPP</jats:styled-content>, control variation in <jats:styled-content style="fixed-case">AGB</jats:styled-content> among 167 plots in intact forest across Amazonia. We then compare these relationships and the observed variation in <jats:styled-content style="fixed-case">AGB</jats:styled-content> and woody <jats:styled-content style="fixed-case">NPP</jats:styled-content> with the predictions of four <jats:styled-content style="fixed-case">DGVM</jats:styled-content>s. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of <jats:styled-content style="fixed-case">AGB</jats:styled-content>, which is consistent with the importance of stand size structure for determining spatial variation in <jats:styled-content style="fixed-case">AGB</jats:styled-content>. The relationship between stem mortality rates and <jats:styled-content style="fixed-case">AGB</jats:styled-content> varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences <jats:styled-content style="fixed-case">AGB</jats:styled-content>. In contrast to previous findings, we find that woody <jats:styled-content style="fixed-case">NPP</jats:styled-content> is not correlated with stem mortality rates and is weakly positively correlated with <jats:styled-content style="fixed-case">AGB</jats:styled-content>. Across the four models, basin‐wide average <jats:styled-content style="fixed-case">AGB</jats:styled-content> is similar to the mean of the observations. However, the models consistently overestimate woody <jats:styled-content style="fixed-case">NPP</jats:styled-content> and poorly represent the spatial patterns of both <jats:styled-content style="fixed-case">AGB</jats:styled-content> and woody <jats:styled-content style="fixed-case">NPP</jats:styled-content> estimated using plot data. In marked contrast to the observations, <jats:styled-content style="fixed-case">DGVM</jats:styled-content>s typically show strong positive relationships between woody <jats:styled-content style="fixed-case">NPP</jats:styled-content> and <jats:styled-content style="fixed-case">AGB</jats:styled-content>. Resolving these differences will require incorporating forest size structure, mechanistic models of stem mortality and variation in functional composition in <jats:styled-content style="fixed-case">DGVM</jats:styled-content>s.</jats:p>
Original languageEnglish
Pages (from-to)3996-4013
Number of pages0
JournalGlobal Change Biology
Volume22
Issue number12
Early online date19 May 2016
DOIs
Publication statusPublished - Dec 2016

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